J/ApJ/795/165 Line ratios in z∼2-3 galaxies from KBSS-MOSFIRE (Steidel+, 2014)
Strong nebular line ratios in the spectra of z∼2-3 star forming galaxies:
first results from KBSS-MOSFIRE.
Steidel C.C., Rudie G.C., Strom A.L., Pettini M., Reddy N.A., Shapley A.E.,
Trainor R.F., Erb D.K., Turner M.L., Konidaris N.P., Kulas K.R., Mace G.,
Matthews K., McLean I.S.
<Astrophys. J., 795, 165 (2014)>
=2014ApJ...795..165S 2014ApJ...795..165S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, IR ; Redshifts ; Abundances ; Spectroscopy ; Surveys
Keywords: cosmology: observations - galaxies: abundances - galaxies: evolution -
galaxies: formation - galaxies: fundamental parameters -
galaxies: high-redshift - galaxies: starburst -
instrumentation: spectrographs
Abstract:
We present initial results of a deep near-IR spectroscopic survey
covering the 15 fields of the Keck Baryonic Structure Survey using the
recently commissioned MOSFIRE spectrometer on the Keck 1 telescope. We
focus on a sample of 251 galaxies with redshifts 2.0<z<2.6, star
formation rates (SFRs) 2≲SFR≲200 M☉/yr, and stellar masses
8.6<log(M*/M☉)<11.4, with high-quality spectra in both
H- and K-band atmospheric windows. We show unambiguously that the
locus of z∼2.3 galaxies in the "BPT" nebular diagnostic diagram
exhibits an almost entirely disjointed, yet similarly tight,
relationship between the line ratios [N II] λ6585/Hα and
[O III]/Hβ as compared to local galaxies. Using photoionization
models, we argue that the offset of the z∼2.3 BPT locus relative to
that at z∼0 is caused by a combination of harder stellar ionizing
radiation field, higher ionization parameter, and higher N/O at a
given O/H compared to most local galaxies, and that the position of a
galaxy along the z∼2.3 star-forming BPT locus is surprisingly
insensitive to gas-phase oxygen abundance. The observed nebular
emission line ratios are most easily reproduced by models in which the
net stellar ionizing radiation field resembles a blackbody with
effective temperature Teff=50000-60000 K, the gas-phase oxygen
abundances lie in the range 0.2<Z/Z☉<1.0, and the ratio of
gas-phase N/O is close to the solar value. We critically assess the
applicability at high redshift of commonly used strong line indices
for estimating gas-phase metallicity, and consider the implications of
the small intrinsic scatter of the empirical relationship between
excitation-sensitive line indices and M*(i.e., the "mass-metallicity"
relation) at z≃2.3.
Description:
All near-IR spectroscopic observations described in this paper were
obtained using the Multi-Object Spectrometer for InfraRed Exploration
(MOSFIRE; McLean et al. 2010, Proc. SPIE, 7735, 77351E; 2012, Proc.
SPIE, 8446, 84460J), the recently commissioned near-IR imaging
spectrometer on the Keck 1 10 mm telescope at the W. M. Keck
Observatory on Mauna Kea. Some of the data were obtained during
MOSFIRE commissioning science verification in 2012 May and June, with
the remainder obtained during early science observations in 2012
September and October and 2013 March, May, June, and November.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 104 168 KBSS-MOSFIRE Galaxies with both [N II]/Hα
and [O III]/Hβ Measurements
table2.dat 103 51 KBSS-MOSFIRE Galaxies with [O III]/Hβ
Measurements and [N II]/Hα Limits
table3.dat 97 32 KBSS-MOSFIRE Galaxies with [N II]/Hα
and Stellar Mass Measurements
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See also:
J/ApJ/706/1364 : SINS survey of high-redshift galaxies
(Forster Schreiber+, 2009)
J/A+A/551/A93 : Nebular emission from z≃2-3 star-forming galaxies
(Guaita+, 2013)
Byte-by-byte Description of file: table1.dat table2.dat table3.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Galaxy name
13- 18 F6.4 --- z Nebular redshift
20- 24 F5.2 [Msun] logM* ? Log of stellar mass
26 A1 --- l_log([NII]/Ha) [<] Limit flag on log([NII]/Ha)
27- 31 F5.2 --- log([NII]/Ha) Line ratio of [N II]/Hα
33- 36 F4.2 --- E_log([NII]/Ha) ? Upper limit uncertainty in
log([NII]/Ha)
38- 41 F4.2 --- e_log([NII]/Ha) ? Lower limit uncertainty in
log([NII]/Ha)
43- 47 F5.2 --- log([OIII]/Hb) ? Line ratio of [O III]/Hβ
49- 52 F4.2 --- E_log([OIII]/Hb) ? Upper limit uncertainty in
log([OIII]/Hb)
54- 57 F4.2 --- e_log([OIII]/Hb) ? Lower limit uncertainty in
log([OIII]/Hb)
59 A1 --- l_12+log(O/H) [<] Limit flag on 12+log(O/H)
60- 63 F4.2 --- 12+log(O/H) Oxygen abundance assuming the N2
calibration of PP04
(Pettini & Pagel, 2004MNRAS.348L..59P 2004MNRAS.348L..59P)
65- 68 F4.2 --- E_12+log(O/H) ? Upper limit uncertainty in 12+log(O/H)
70- 73 F4.2 --- e_12+log(O/H) ? Lower limit uncertainty in 12+log(O/H)
75 A1 --- l_12+log(O/H)O3 [<] Limit flag on 12+log(O/H)O3
76- 79 F4.2 --- 12+log(O/H)O3 ? Oxygen abundance assuming the O3N2
calibration of PP04
(Pettini & Pagel, 2004MNRAS.348L..59P 2004MNRAS.348L..59P)
81- 84 F4.2 --- E_12+log(O/H)O3 ? Upper limit uncertainty in
12+log(O/H)O3
86- 89 F4.2 --- e_12+log(O/H)O3 ? Lower limit uncertainty in
12+log(O/H)O3
91-104 A14 --- Notes Notes (1)
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Note (1): Note as follows:
A1 = Object identified as an AGN on the basis of both rest-UV (LRIS-B) and
rest-optical (MOSFIRE) spectra;
A2 = Object identified as an AGN on the basis of near-IR (MOSFIRE) spectra;
1 = Objects with optical (rest-UV) spectra obtained using Keck/LRIS-B;
galaxies whose LRIS-B spectra yielded spectroscopic redshifts are marked
1, while 1a denotes objects that were attempted spectroscopically in the
rest-UV without yielding a secure spectroscopic redshift;
2 = Erb et al. (2003ApJ...591..101E 2003ApJ...591..101E);
3 = Shapley et al. (2005ApJ...626..698S 2005ApJ...626..698S);
4 = Erb et al. (2006ApJ...646..107E 2006ApJ...646..107E);
5 = Law et al. (2009ApJ...697.2057L 2009ApJ...697.2057L);
6 = Steidel et al. (2010ApJ...717..289S 2010ApJ...717..289S);
7 = Forster Schreiber et al. (2009, J/ApJ/706/1364);
8 = Erb et al. (2010ApJ...719.1168E 2010ApJ...719.1168E);
9 = Law et al. (2012Natur.487..338L 2012Natur.487..338L);
10 = Shapley et al. (2004ApJ...612..108S 2004ApJ...612..108S).
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 24-May-2017